Thin film transistor liquid crystal display devices (TFT-LCDs) are a main kind of flat panel display devices (FPDs).
Based on the direction of the electrical field for driving the liquid crystal material, TFT-LCDs can be divided into a vertical field type and a horizontal field type. For the vertical field type TFT-LCDs, it is necessary to form pixel electrodes on an array substrate and form common electrodes on a color filter substrate. However, for the horizontal field type TFT-LCD, it is necessary to form both pixel electrodes and common electrodes on the array substrate. As a result, during manufacturing the array substrate of a horizontal field type TFT-LCD, as compared with the array substrate of a vertical field type TFT-LCD, one additional masking process for forming the common electrodes is required. The vertical field type TFT-LCDs include twist nematic (TN) type TFT-LCDs; the horizontal field type TFT-LCDs include fringe field switching (FFS) type TFT-LCDs and in-plane switching (IPS) type TFT-LCDs. The horizontal field type TFT-LCDs, especially FFS type TFT-LCDs, have advantages of wide viewing angle, high aperture ratio and the like, and are applied widely to the field of the liquid crystal display device.
Currently, the array substrate of an FFS type TFT-LCD is manufactured by forming structural patterns with a plurality of patterning processes, each of which in turn comprises processes of exposing photoresist by using a mask, developing, etching, removing the remaining photoresist, and the like. The etching process may comprise dry etching and wet etching. Therefore, the complexity of the process for manufacturing the array substrate of a TFT-LCD is evaluated by the number of patterning processes, and thus reducing of the number of pattern processes would result in a decreased cost. The six-pattern-process for manufacturing the array substrate of an FFS type TFT-LCD in the prior art comprises: patterning of a common electrode, patterning of gate lines and gate electrodes, patterning of an active layer, patterning of source electrodes/drain electrodes, patterning of via holes, and patterning of pixel electrodes.
The four-pattern-processes in the prior art for manufacturing the array substrate of an FFS type TFT-LCD is conducted as follows.
Step 1, depositing a first metal film, and forming patterns of gate lines, common electrodes and gate electrodes by a first patterning process by using an ordinary mask plate;
Step 2, depositing a gate insulating film and an active layer (a semiconductor layer and an impurity-doped semiconductor layer) film, and forming patterns of the active layer by a second patterning process by using an ordinary mask plate;
Step 3, sequentially depositing a first transparent conductive film and a second metal film, and forming patterns of pixel electrodes, source electrodes, drain electrodes and TFT channels by a third patterning process by using a dual-tone mask plate; and
Step 4, depositing a passivation layer and a second transparent conductive layer, and forming patterns of the passivation layer, connection holes (for connecting the common electrodes and the common electrode lines), connection holes in a PAD region (the PAD region is a region for bonding wires of a driving circuit board to the array substrate, and the wires can be connected electrically to the gate lines, the data lines, the common electrode lines and the like through the connection holes in the PAD region), and the common electrodes by a fourth patterning process by using a dual-tone mask plate.